In our system for recording and transmitting lectures over the Internet the board
content is sent as vector graphics, yielding a high quality image, while the video
of the lecturer is sent as a separate stream. It is easy for the viewer to read the
board, but the lecturer appears in a separate window. To eliminate this problem,
we segment the lecturer from the video stream and paste his image on the board
image at video stream rates. The lecturer can be dimmed by the remote viewer
from opaque to semitransparent, or even transparent. This paper explains the two
techniques we apply to achieve this: texture classification based segmentation, and
segmentation using a novel 3D camera based on the time-of-flight of backscattered
light principle. We argue that this technique provides a solution to the divided
attention problem which arises when board and lecturer are transmitted in two
different streams.